Revolving algal biofilm photobioreactor systems and methods

ABSTRACT

An algal growth system can include a vertical reactor that can include a flexible sheet material, where the flexible sheet material can be configured to facilitate the growth and attachment of algae. The vertical reactor can include a shaft, where the shaft can be associated with and can supports the flexible sheet material and a drive motor, where the drive motor can be coupled with the shaft such that the flexible sheet material can be selectively actuated. The algal growth system can include a raceway pond, where the vertical reactor can be positioned at least partially within the raceway pond, where the raceway pond can include a fluid reservoir, where the flexible sheet material can be configured to pass through the fluid reservoir during operation of the algal growth system, a contacting liquid, where the contacting liquid can be retained within the fluid reservoir and can includes nutrients that facilitate the growth of the algae, and a liquid phase and a gaseous phase, where the liquid phase can include rotating the flexible sheet material through the contacting liquid retained in the fluid reservoir and the gaseous phase can include rotating the flexible sheet material through gaseous carbon dioxide.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. non-provisional patentapplication Ser. No. 14/212,479, filed Mar. 14, 2014, which claims thepriority benefit of U.S. provisional patent application Ser. No.61/783,737, filed Mar. 14, 2013, and hereby incorporates the sameapplications herein by reference in their entirety.

TECHNICAL FIELD

Embodiments of the technology relate, in general, to biofilm technology,and in particular to a revolving algal biofilm photobioreactor (RABP)for simplified biomass harvesting.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily understood from a detaileddescription of some example embodiments taken in conjunction with thefollowing figures:

FIG. 1 depicts a flow chart illustrating considerations that may need tobe addressed by example embodiments described herein.

FIG. 2 depicts a top view of microalgae being grown on polystyrene foam.

FIG. 3 depicts a perspective view of an example embodiment of arevolving algal biofilm photobioreactor.

FIG. 4 depicts a schematic front view of the revolving algal biofilmphotobioreactor shown in FIG. 3.

FIG. 5 depicts a top view of microalgae being grown on a variety ofmaterials.

FIG. 6 depicts a bar chart of harvesting frequencies for an algalstrain.

FIG. 7 depicts a perspective view of a straight vertical reactoraccording to one embodiment.

SUMMARY

An algal growth system can include a vertical reactor that can include aflexible sheet material, where the flexible sheet material can beconfigured to facilitate the growth and attachment of algae. Thevertical reactor can include a shaft, where the shaft can be associatedwith and can supports the flexible sheet material and a drive motor,where the drive motor can be coupled with the shaft such that theflexible sheet material can be selectively actuated. The algal growthsystem can include a raceway pond, where the vertical reactor can bepositioned at least partially within the raceway pond, where the racewaypond can include a fluid reservoir, where the flexible sheet materialcan be configured to pass through the fluid reservoir during operationof the algal growth system, a contacting liquid, where the contactingliquid can be retained within the fluid reservoir and can includesnutrients that facilitate the growth of the algae, and a liquid phaseand a gaseous phase, where the liquid phase can include rotating theflexible sheet material through the contacting liquid retained in thefluid reservoir and the gaseous phase can include rotating the flexiblesheet material through gaseous carbon dioxide.

A method of growing algae can include the step of providing an algalgrowth system that can include a vertical reactor that can include aflexible sheet material, where the flexible sheet material can beconfigured to facilitate the growth and attachment of algae. Thevertical reactor can include a shaft, where the shaft can be associatedwith and can supports the flexible sheet material and a drive motor,where the drive motor can be coupled with the shaft such that theflexible sheet material can be selectively actuated. The algal growthsystem can include a raceway pond, where the vertical reactor can bepositioned at least partially within the raceway pond, where the racewaypond can include a fluid reservoir, where the flexible sheet materialcan be configured to pass through the fluid reservoir during operationof the algal growth system, a contacting liquid, where the contactingliquid can be retained within the fluid reservoir and can includesnutrients that facilitate the growth of the algae. The method of growingalgae can include rotating the flexible sheet material of the algalgrowth system through a liquid phase such that the flexible sheetmaterial passes through the contacting liquid retained in the fluidreservoir, rotating the flexible sheet material of the algal growthsystem through a gaseous phase such that the flexible sheet materialpasses through gaseous carbon dioxide, and harvesting the algae from theflexible sheet material.

DETAILED DESCRIPTION

Various non-limiting embodiments of the present disclosure will now bedescribed to provide an overall understanding of the principles of thestructure, function, and use of the proficiency tracking systems andprocesses disclosed herein. One or more examples of these non-limitingembodiments are illustrated in the accompanying drawings. Those ofordinary skill in the art will understand that systems and methodsspecifically described herein and illustrated in the accompanyingdrawings are non-limiting embodiments. The features illustrated ordescribed in connection with one non-limiting embodiment may be combinedwith the features of other non-limiting embodiments. Such modificationsand variations are intended to be included within the scope of thepresent disclosure.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “some example embodiments,” “one exampleembodiment,” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with any embodimentis included in at least one embodiment. Thus, appearances of the phrases“in various embodiments,” “in some embodiments,” “in one embodiment,”“some example embodiments,” “one example embodiment,” or “in anembodiment” in places throughout the specification are not necessarilyall referring to the same embodiment. Furthermore, the particularfeatures, structures or characteristics may be combined in any suitablemanner in one or more embodiments.

Traditionally, algae are grown in open raceway ponds or enclosedphotobioreactors, where algae cells are in suspension and are harvestedthrough sedimentation, filtration, or centrifugation. Due to the smallsize (3-30 μm) of algae cells and the dilute algae concentration (<1%w/v), gravity sedimentation of suspended cells often takes a long timein a large footprint settling pond. Filtration of algal cells from theculture broth can result in filter fouling. Centrifugation can achievehigh harvest efficiency; however, the capital investment and operationalcost for a centrifugation system can be prohibitively expensive. Due tothese drawbacks, an alternative method for harvesting and dewateringalgae biomass may be advantageous.

Described herein are example embodiments of revolving algal biofilmphotobioreactor systems and methods that can simplify biomassharvesting. In one example embodiment, systems and methods can providecost effective harvesting of algae biomass. In some embodiments, systemsand methods can be used to produce algae for both biofuel feedstock andaquacultural feed sources. In some embodiments, algal cells can beattached to a material that can be rotated between a nutrient-richliquid phase and a carbon dioxide rich gaseous phase such thatalternative absorption of nutrients and carbon dioxide can occur. Thealgal cells can be harvested by scrapping from the surface to which theyare attached, which can eliminate harvest procedures commonly used insuspension cultivation systems, such as sedimentation or centrifugation.It will be appreciated that systems and methods described herein can becombined with sedimentation, centrifugation, or any other suitableprocesses.

The examples discussed herein are examples only and are provided toassist in the explanation of the apparatuses, devices, systems andmethods described herein. None of the features or components shown inthe drawings or discussed below should be taken as mandatory for anyspecific implementation of any of the apparatuses, devices, systems ormethods unless specifically designated as mandatory. For ease of readingand clarity, certain components, modules, or methods may be describedsolely in connection with a specific figure. Any failure to specificallydescribe a combination or sub-combination of components should not beunderstood as an indication that any combination or sub-combination isnot possible. Also, for any methods described, regardless of whether themethod is described in conjunction with a flow diagram, it should beunderstood that unless otherwise specified or required by context, anyexplicit or implicit ordering of steps performed in the execution of amethod does not imply that those steps must be performed in the orderpresented but instead may be performed in a different order or inparallel.

Example embodiments described herein can mitigate air and waterpollution while delivering high value bio-based products and animalfeeds from microalgae. Example embodiments of RABP technology can play acritical role in creating an algal culture system that can economicallyproduce algae biomass for, for example, biofuel production andaquacultural feed production. Microalgae may have a significant impactin the renewable transportation fuels sector. Example embodiments cangrow microalgae that can be used in biofuel production with a lowharvest cost. Algae, if produced economically, may also serve as aprimary feed source for the US aquaculture industry.

Example systems and methods can include developing a biofilm-basedmicroalgae cultivation system (RABP) that could be widely adapted by themicroalgae industry for producing, for example, fuels and high valueproducts. Over the past few years microalgae has been rigorouslyresearched as a promising feedstock for renewable biofuel production.Microalgae use photosynthesis to transform carbon dioxide and sunlightinto energy. This energy is stored in the cell as oils, which have ahigh energy content. The oil yield from algae can be significantlyhigher than that from other oil crops. Algae oil can generally be easilyconverted to biodiesel and could replace traditional petroleum-baseddiesel. In addition to fuel production, microalgae have also beenrigorously researched for the potential to produce various high valueproducts such as animal feed, omega-3 polyunsaturated fatty acids,pigments, and glycoproteins.

Referring to FIG. 1, in spite of the strong potential of microalgae invarious applications, the high cost of algae production can still be themajor limitation in industrial scale operation. According to the UnitedStates Department of Energy's final report on the Aquatic SpeciesProgram and the recent National Algal Biofuel Technology Roadmap, thereare three main areas that may need to be focused on in order to makealgae cultivation economically viable, including strain development,control of contamination by native species, and reducing the high costof biomass harvesting and dewatering. Example embodiments may minimizethe cost associated with biomass harvesting and dewatering of algalcells from an aqueous culture system.

Generally, research on algae cultivation is done using suspended algaeculture. This culture method can have drawbacks including the issue withharvesting. Example embodiments can promote a simple economicalharvesting method. Example embodiments can include a mechanizedharvesting system, which can remove concentrated algae in-situ from anattachment material and can minimize the amount of de-watering neededpost-harvest. Example embodiments can optimize gas mass transfer, wheregrowth in an enclosed greenhouse 40 may provide the ability to increaseCO2 concentration inside the reactor. Generally, at higher CO2concentrations, the growth rate of algae will increase. Exampleembodiments can utilize minimal growth medium, where the triangulardesign in example embodiments may reduce the chemical costs of growthmedium and may reduce the total water needed for the growth. In oneembodiment, such advantages may be accomplished by submerging only thelowest elevated corner of a triangle system needs into the medium.

Referring to FIG. 2, microalgae can be grown on the surface ofpolystyrene foam. FIG. 2 illustrates how algae can be harvested byscraping the surface of the foam. The mechanical separation can resultin biomass with water content similar to centrifuged samples and theresidual biomass left on the surface can serve as an ideal inoculum forsubsequent growth cycles. However, such systems can be limited by theuse of polystyrene foam which is not a renewable and environmentalfriendly material. The rigidity of the styrene foam may also limit itsapplication in embodiments of rotational systems and methods describedherein.

Referring to FIGS. 3 and 4, an example embodiment of a revolving algalbiofilm Photobioreactor (RABP) 10, in which the algal cells 18 can beattached to a solid surface of a supporting material 12, is disclosed.The system can keep the algal cells fixed in place and can bringnutrients to the cells, rather than suspend the algae in a culturemedium. As shown in FIGS. 3 and 4, algal cells can be attached to amaterial 12 that is rotating between a nutrient-rich liquid phase 15 anda CO2-rich gaseous phase 16 for alternative absorption of nutrients andCO2. The algal biomass can be harvested by scrapping the biomass fromthe attached surface with a harvesting squeegee 20 (FIG. 4) or othersuitable device or system. In example embodiments, the naturallyconcentrated biofilm can be in-situ harvested during the cultureprocess, rather than using an additional sedimentation or flocculationstep for harvesting, for example. The culture can enhance the masstransfer by directly contacting algal cells with CO2 molecules ingaseous phase, where traditional suspended culture systems may have torely on the diffusion of CO2 molecules from gaseous phase to the liquidphase, which may be limited by low gas-liquid mass transfer rate.Example embodiments may only need a small amount of water by submergingthe bottom of the triangle 22 in liquid 14 while maximizing surface areafor algae to attach. Example embodiments can be scaled up to anindustrial scale because the system may have a simple structure and canbe retrofit on existing raceway pond systems 102 (FIG. 7). Exampleembodiments can be used in fresh water systems and can be adapted tosaltwater culture systems. For example, embodiments of this system canbe placed in the open ocean instead of in a raceway pond reactor. Inthis example application, the ocean can naturally supply the algae withsufficient sunlight, nutrient, water, and CO2, which in turn maydecrease operational costs.

Still referring to FIGS. 3 and 4, embodiments of the system can includea drive motor 24, a gear system 26 that can rotate drive shafts 28,drive shafts 28 that can rotate a flexible material 12, a flexible sheetmaterial 12 that can rotate into contact with liquid 14 and can allowalgae 18 to attach thereto. The motor 24 can include a gear system 26 orpulley system that can drive one or a plurality of shafts 28, where theshafts 28 can rotate the flexible sheet material 12 in and out of acontacting liquid 14, for example. Embodiments can also include a liquidreservoir 30, mister, water dripper, or any other suitable component ormechanism that can keep algae, which can be attached to the flexiblesheet material 12, moist. Embodiments can include any suitable scrapingsystem, vacuum system or mechanism for harvesting the algae 18 from theflexible sheet material 12.

In an example embodiment, a generally triangular system 22 can beprovided. Such a configuration can be beneficial in maximizing theamount of sunlight algae is exposed to. However versions of the systemcan be designed, for example, in any configuration that includes a“sunlight capture” part 32 which can be exposed to air and sunlight, anda “nutrient capture” part 34 which can be submerged into a nutrientsolution. A straight vertical design is contemplated, which may be thesimplest and most cost efficient design because such a system mayminimize the amount of wasted space and may maximize the amount of algaeproduced in a small area by growing this system vertically. Alternativedesigns can include a straight vertical reactor 100, a reactor that isstraight but slightly angled to provide more surface area for sunlightto hit, a cylindrical reactor, or a square shaped reactor.

Referring to FIG. 5, any suitable material 12, such as any suitableflexible fabric, can be used with the systems and methods describedherein to grow any suitable material. For example, the microalgaChlorella, such as Chlorella vulgaris can be grown on materials such as,muslin cheesecloth, armid fiberglass, porous PTFE coated fiberglass,chamois, vermiculite, microfiber, synthetic chamois, fiberglass, burlap,cotton duct, velvet, Tyvek, polylactic acid, abrased polylactic acid,vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen,cashmere, leather, silk, lyocell, hemp fabric, Spandex, polyurethane,olefin fiber, polylactide, Lurex, carbon fiber, and combinationsthereof.

It will be appreciated that any suitable algal strain 18 (includingcyanobacteria) as well as fungal strains, such as strains that can beused in aquaculture feed, animal feed, nutraceuticals, or biofuelproduction can be used. Such strains can include Nannochloropsis sp.,which can be used for both biofuel production and aquacultural feed;Scenedesmus sp., a green microalga that can be used in wastewatertreatment as well as for fuel production feedstock; Haematococcus sp,which can produce a high level of astaxanthin; Botryococcus sp. a greenmicroalga with high oil content; Spirulina sp. a blue-green alga withhigh protein content; Dunaliella sp. a green microalga containing alarge amount of carotenoids; a group of microalgae species producing ahigh level of long chain polyunsaturated fatty acids can includeArthrospira, Porphyridium, Phaeodactylum, Nitzschia, Crypthecodinium andSchizochytrium. Any suitable parameter, including gaseous phase CO2concentration, harvesting frequency, the rotation speed of the RABPreactor, the depth of the biofilm harvested, the ratio of submergedportion to the air-exposure portion of the RABP reactor, or the gapbetween the different modules of the RABP system can be optimized forany suitable species.

Referring to FIG. 6, any harvesting schedule can be used in accordancewith example embodiments described herein. The mechanism of harvestingbiomass from the biofilm can be, for example, scraping or vacuum.Biomass productivity may vary by species and any suitable harvestingtime is contemplated to maximize such productivity. For example, asshown in FIG. 6, of this specific species as a function of harvestingtime by growing the algae on a RABP system then harvesting the cells atdifferent durations. As shown in FIG. 6, for Chlorella the optimalharvest frequency may be every 7 days. In example embodiments, managingother parameters such as CO2 concentration and nutrient loading may alsoimpact algal growth performance.

In various embodiments disclosed herein, a single component can bereplaced by multiple components and multiple components can be replacedby a single component to perform a given function or functions. Exceptwhere such substitution would not be operative, such substitution iswithin the intended scope of the embodiments.

Some of the figures can include a flow diagram. Although such figurescan include a particular logic flow, it can be appreciated that thelogic flow merely provides an exemplary implementation of the generalfunctionality. Further, the logic flow does not necessarily have to beexecuted in the order presented unless otherwise indicated. In addition,the logic flow can be implemented by a hardware element, a softwareelement executed by a computer, a firmware element embedded in hardware,or any combination thereof.

The foregoing description of embodiments and examples has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or limiting to the forms described. Numerous modificationsare possible in light of the above teachings. Some of thosemodifications have been discussed, and others will be understood bythose skilled in the art. The embodiments were chosen and described inorder to best illustrate principles of various embodiments as are suitedto particular uses contemplated. The scope is, of course, not limited tothe examples set forth herein, but can be employed in any number ofapplications and equivalent devices by those of ordinary skill in theart. Rather it is hereby intended the scope of the invention to bedefined by the claims appended hereto.

We claim:
 1. An algal growth system comprising: (a) a vertical reactorcomprising; (i) a flexible sheet material, the flexible sheet materialbeing configured to facilitate the growth and attachment of algae; (ii)a shaft, wherein the shaft is associated with and supports the flexiblesheet material; and (iii) a drive motor, the drive motor being coupledwith the shaft such that the flexible sheet material is selectivelyactuated; (b) a raceway pond, the vertical reactor being positioned atleast partially within the raceway pond, the raceway pond comprising;(i) a fluid reservoir, wherein the flexible sheet material is configuredto pass through the fluid reservoir during operation of the algal growthsystem; and (ii) a contacting liquid, wherein the contacting liquid isretained within the fluid reservoir and includes nutrients thatfacilitate the growth of the algae; and (c) a liquid phase and a gaseousphase, wherein the liquid phase comprises rotating the flexible sheetmaterial through the contacting liquid retained in the fluid reservoirand the gaseous phase comprises rotating the flexible sheet materialthrough gaseous carbon dioxide.
 2. The algal growth system of claim 1,further comprising a harvesting mechanism.
 3. The algal growth system ofclaim 1, wherein the harvesting mechanism is a squeegee.
 4. The algalgrowth system of claim 1, wherein the flexible sheet material isselected from the group consisting of cheesecloth, fiberglass, porousPTFE coated fiberglass, chamois, vermiculite, microfiber, syntheticchamois, burlap, cotton duct, velvet, vinyl laminated nylon, polyester,wool, acrylic, lanolin, woolen, cashmere, leather, silk, lyocell, hempfabric, polyurethane, olefin fiber, polylactide, and carbon fiber. 5.The algal growth system of claim 1, wherein the algae is selected fromthe group consisting of Nannochloropsis, Scenedesmus, Haematococcus,Botryococcus, Spirulina, Dunaliella, Arthrospira, Porphyridium,Phaeodactylum, Nitzschia, Crypthecodinium and Schizochytrium.
 6. Thealgal growth system of claim 1, further comprising an enclosedgreenhouse.
 7. The algal growth system of claim 6, wherein the enclosedgreenhouse has a higher carbon dioxide concentration than theatmosphere.
 8. The algal growth system of claim 1, wherein the drivemotor is configured to rotate the flexible sheet material on apredetermined schedule.
 9. The algal growth system of claim 1, whereinthe flexible sheet material is a biofilm.
 10. The algal growth system ofclaim 1, wherein the flexible sheet material is configured to grow andretain the algae until the algae is physically removed.
 11. The algalgrowth system of claim 1, wherein the algal growth system is configuredfor industrial use.
 12. A method of growing algae comprising the stepsof: providing an algal growth system comprising; (a) a vertical reactorcomprising; (i) a flexible sheet material, the flexible sheet materialbeing configured to facilitate the growth and attachment of algae; (ii)a shaft, wherein the shaft is associated with and supports the flexiblesheet material; and (iii) a drive motor, the drive motor being coupledwith the shaft such that the flexible sheet material is selectivelyactuated; and (b) a raceway pond, the vertical reactor being positionedat least partially within the raceway pond, the raceway pond comprising;(i) a fluid reservoir, wherein the flexible sheet material is configuredto pass through the fluid reservoir during operation of the algal growthsystem; and (ii) a contacting liquid, wherein the contacting liquid isretained within the fluid reservoir and includes nutrients thatfacilitate the growth of the algae; rotating the flexible sheet materialof the algal growth system through a liquid phase such that the flexiblesheet material passes through the contacting liquid retained in thefluid reservoir; rotating the flexible sheet material of the algalgrowth system through a gaseous phase such that the flexible sheetmaterial passes through gaseous carbon dioxide; and harvesting the algaefrom the flexible sheet material.
 13. The method of growing algae ofclaim 12, wherein the algal growth system further comprises an enclosedgreenhouse.
 14. The method of growing algae of claim 12, wherein thealgae is selected from the group consisting of Nannochloropsis,Scenedesmus, Haematococcus, Botryococcus, Spirulina, Dunaliella,Arthrospira, Porphyridium, Phaeodactylum, Nitzschia, Crypthecodinium andSchizochytrium.
 15. The method of growing algae of claim 12, wherein theflexible sheet material is selected from the group consisting ofcheesecloth, fiberglass, porous PTFE coated fiberglass, chamois,vermiculite, microfiber, synthetic chamois, burlap, cotton duct, velvet,vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen,cashmere, leather, silk, lyocell, hemp fabric, polyurethane, olefinfiber, polylactide, and carbon fiber.
 16. The method of growing algae ofclaim 12, wherein the algal growth system is configured for industrialuse.
 17. The method of growing algae of claim 12, further comprising thestep of rotating the algal growth system according to a predeterminedschedule.